> Responses like this violate the rules for the site and undermine HN as a place of discussion. I would love to hear a real argument.
You don't deserve a real argument. "Why not require reel mowers?" isn't a serious question. Figuring out an answer takes only a few moments of thought, or reading the first section of the law in question, wherein the legislature lays out the rationale and justification for the regulation. (The whole law is just over 600 words, so reading it is quick and easy.) The question is just a cheap rhetorical trick.
If you actually have trouble coming up with an answer to that question, or if you think banning all forms of powered mowers would actually be a sensible public policy, then you're welcome to share your thoughts on the matter in more detail. Until then, there's no reason for anyone to take such a silly and provocative question at face value.